Dynamic interaction between vortices, antivortices and holes in domain walls investigated by means of time resolved Photoemission Electron Microscopy (PEEM)

In this work we study the interaction of vortex cores with either holes in domain walls of Landau structures or other vortices and antivortices, which are also interconnected through the adjacent domain walls of a single cross-tie structure.
During the last few years the investigation of magnetic vortices and their dynamic properties has attracted great attention due to the fundamental interest in the physics of solitons and since they might be used as non volatile memory devices in future applications, e. g. [1,2]. One striking feature of magnetic vortices is that the cores are attracted and can be trapped by artificial defects. If more than one of such defects are created a switching between different vortex core trapped states, which might serve as discrete levels in a multivalent memory device, can be achieved. We report the imaging of the magnetic excitation spectrum in presence of holes, fabricated by focused ion beam milling, in the magnetic domains and domain walls of Landau structures by means of x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM). The vortex core in the center of the structure is not modified by ions, here we investigate the interaction of unmodified vortex cores with holes far away (> 1 Mikrometer) in the domain walls and the domains of Landau structures. Due to the very high lateral and temporal resolution the magnetization dynamics and the corresponding Eigen modes (Fig. 1), which are characteristic for the vortex-hole interaction, are investigated in detail [3]. Analyzing the vortex movement unravels an acceleration of the vortex gyrotropic mode if holes are present in the middle of domain walls. The presence of holes in the middle of domains has no significant influence on the vortex speed. The experimental results are compared to micromagnetic simulations.

References:

[1] S. B. Choe et al., Science 304, 420 (2004), J. Raabe et al., Phys. Rev. Lett. 94, 217204 (2005).
[2] B. van Waeyenberge et al., Nature 444, 461 (2006)
[3] K. Kuepper et al., manuscript in preparation.
[4] K. Kuepper et al., Phys. Rev. Lett. 99, 167202 (2007)